Method and apparatus to allocate radio resources for transmitting a message part in an enhanced rach

ABSTRACT

A method and apparatus for allocating resources to a wireless transmit receive unit (WTRU) includes the WTRU transmitting a signature sequence to a Node B, receiving an acknowledge signal from the Node B, and determining a default resource index. The resource index is associated with enhanced dedicated channel (E-DCH) parameters.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/238,546, filed on Sep. 26, 2008, which claims the benefit of U.S.Provisional Application No. 60/975,715, filed on Sep. 27, 2007, both ofwhich are incorporated herein by reference as if fully set forth.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

In many cellular communications systems, the access to radio resourcesis controlled by the radio network. When a wireless transmit/receiveunit (WTRU) has data to transmit to the network, it acquires radioresource access before transmitting its data payload. To achieve this ina 3rd Generation Partnership Project (3GPP) network, for example, a WTRUmust gain access to the random access channel (RACH). Access to the RACHis contentious and there are mechanisms to reduce the probability ofcollision, that is, when two WTRUs are accessing the resourcesimultaneously.

Procedures for random access include a preamble phase with power ramp-upfollowed by channel acquisition information and message transmission.Because of the contentious nature of the RACH, to avoid WTRUs holdingthe shared radio resource for a long time, and because there is no powercontrol, relatively short message payloads are transmitted on the RACH,leading to a relatively small data rate. Therefore, the RACH isgenerally used for the transmission of short control messages.Typically, WTRUs demanding larger data rates would be configured by thenetwork to use dedicated resources.

While the data rate provided by the RACH is sufficient for thetransmission of short control messages typical of networks supportingmostly speech communications, it is inefficient for the transmission ofdata messages associated with non-real-time data services, such asinternet browsing, e-mail, and the like. For these data services, thetraffic is bursty by nature and long periods of inactivity may existbetween successive transmissions. For some applications requiringfrequent transmission of keep-alive messages, for example, this mayresult in an inefficient utilization of dedicated resources. Therefore,it may be advantageous for the network to use shared resources for datatransmission instead. The difficulty however, resides in the low datarate offered by the existing RACH.

FIG. 1 shows RACH access with an enhanced dedicated channel (E-DCH) 100in accordance with the prior art. A RACH access with E-DCH 100,hereafter “E-RACH”, may include a RACH preamble phase 102, initialresource assignment 104, collision detection and resolution 106, anE-RACH message part 108, and release of resources 110 or transition toother state. It would be desirable to have a set of mechanisms forefficient use of the E-DCH on the E-RACH.

SUMMARY

A method and apparatus is disclosed for high speed transmission over anE-RACH. This may include a WTRU transmitting a signature sequence,receiving an acknowledge signal in response to the signature sequenceand determining a default resource index. The resource index may beassociated with enhanced dedicated channel (E-DCH) parameters. The WTRUmay also index a set of resource parameters based on the signaturesequence and a scrambling code index

Also disclosed is a method and apparatus for allocating resources to aWTRU. This may include the WTRU receiving a list of resources over abroadcast channel, wherein the list of resources includes a resourceallocation table.

The WTRU may also receive an allocation message. The allocation messagemay include a subset of a resource allocation configuration. The WTRUmay also receive a balance of a resource allocation configuration in abroadcast channel.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description, given by way of example and to be understood inconjunction with the accompanying drawings wherein:

FIG. 1 shows RACH access with E-DCH in accordance with the prior art;

FIG. 2 shows an example wireless communication system including aplurality of wireless transmit/receive units (WTRUs) and a base stationin accordance with one embodiment;

FIG. 3 is a functional block diagram of a WTRU and the base station ofFIG. 2 in accordance with one embodiment;

FIG. 4 is a flow diagram showing a RACH method in accordance with oneembodiment;

FIG. 5 shows a preamble pattern in accordance with one embodiment; and

FIG. 6 shows an acquisition indicator channel (AICH) structure inaccordance with one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

When referred to hereafter, the term “wireless transmit/receive unit(WTRU)” includes, but is not limited to, a user equipment (UE), a mobilestation, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the term “base station” includes, but is notlimited to, a Node B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment. When referred to herein, the terminology “acquisitionindicator channel (AICH) includes, but is not limited to, the AICH, theE-AICH, or any other acquisition indicator type of channel. Whenreferred to herein, the terminology medium access control (MAC) protocoldata unit (PDU) includes, but is not limited to, a MAC-e PDU, a MAC-iPDU, or any other type of MAC-level PDU that is passed on to a higherlayer.

An enhanced random access channel (E-RACH) may use a subset of thefunctionality offered by an enhanced dedicated channel (E-DCH). FIG. 2shows a wireless communication system 200 including a plurality of WTRUs210 and a base station 220. As shown in FIG. 2, the WTRUs 210 are incommunication with the base station 220. Although three (3) WTRUs 210and one (1) base station 220 are shown in FIG. 2, it should be notedthat any combination of wireless and wired devices may be included inthe wireless communication system 200. Each WTRU 210 may communicatewith the station 220 over an E-RACH.

FIG. 3 is a functional block diagram 300 of a WTRU 210 and the basestation 220 of the wireless communication system 200 of FIG. 2. As shownin FIG. 2, the WTRU 210 is in communication with the base station 220.The WTRU is configured to communicate over an enhanced random accesschannel (E-RACH).

In addition to the components that may be found in a typical WTRU, theWTRU 210 includes a processor 315, a receiver 316, a transmitter 317,and an antenna 318. The processor 315 is configured to perform allprocessing required for the WTRU 210 to communicate over an E-RACH. Thereceiver 316 is configured to receive signals from the base station 220and the transmitter 317 is configured to transmit signals over theE-RACH. The receiver 316 and the transmitter 317 are in communicationwith the processor 315. The antenna 318 is in communication with boththe receiver 316 and the transmitter 317 to facilitate the transmissionand reception of wireless data.

In addition to the components that may be found in a typical basestation, the base station 220 includes a processor 325, a receiver 326,a transmitter 327, and an antenna 328. The receiver 326 is configured toreceive signals over the E-RACH and the transmitter 327 is configured totransmit signals to the WTRU 210. The receiver 326 and the transmitter327 are in communication with the processor 325. The antenna 328 is incommunication with both the receiver 326 and the transmitter 327 tofacilitate the transmission and reception of wireless data.

After a WTRU transmits a RACH preamble phase, the WTRU may be configuredfor radio transmission by the UMTS terrestrial radio access network(UTRAN). While some parameters are fixed and common to all WTRUs, someradio resources need to be allocated when the access is granted becauseof the scarcity of those resources.

Different resources may be allocated for the E-RACH transmission phase,including, for example, an uplink (UL) scrambling code, downlink (DL)forward dedicated physical channel (F-DPCH) code, offset, slot format,enhance relative grant channel (E-RGCH) from the serving cell andnon-serving cells for support of soft-handover, and enhanced hybridautomatic retransmission request (HARQ) indicator channel (E-HICH) codeand signatures, enhanced absolute grant channel (E-AGCH) code, enhancedradio network temporary identifier (E-RNTI), and the like.

Resources may be allocated based on implicit rules involving knownparameters at both the WTRU and at a Node B. For example, the enhancedphysical random access channel (E-PRACH) scrambling code index, and thesignature sequence index which was acknowledged on the acquisitionindicator channel (AICH) by the Node B may be known and may be used toindex a set of parameters. Similarly, the access slot, access class andother parameters can be used for the implicit allocation.

Alternatively, there may be one E-RACH message part transmission at atime per E-PRACH. The network may broadcast a list of E-RACH resourcesthat may be shared by all WTRUs. The E-RACH resources may be broadcast,for example, in a short resource allocation table transmitted on thebroadcast channel in the system information block (SIB) or during WTRUconfiguration. Each row of the table may include the radio resourceparameters to be used by the WTRU for its E-RACH message parttransmission on the corresponding E-PRACH. There may be a one-to-manymapping between the PRACH resource and the E-RACH resources. In otherwords, a PRACH may be associated with more than one set of E-RACHresources, but the converse is not allowed. Alternatively, the WTRU canselect the E-RACH resources and determine the PRACH from the mapping ofa PRACH to E-RACHs.

When a WTRU gets access to the E-PRACH, such as via an ACK on thecorresponding AICH, for example, it may use those resources for itsE-RACH message part transmission. If the E-PRACH resource is busy, theNode B may send a NACK on the AICH, triggering a backoff mechanism atthe WTRU.

Alternatively, a longer lookup table could be used for resourceallocation. This table could be populated using predefined rules so thatentries would not need to be transmitted explicitly. Each row of thetable may include the resources used for the transmission of the E-RACHmessage part.

Since the table may be longer than the maximum number of E-PRACHsavailable, other indexing parameters may be used. Such parameters mayinclude, for example, the signature sequence index, access slot index,and time index.

When a WTRU gets access to the E-PRACH via an ACK on the correspondingAICH, it determines the E-RACH resources by looking at the correspondingrow in the table. If the resulting E-PRACH resource is busy, the Node Bmay send a NACK on the AICH, triggering the backoff mechanism at theWTRU.

Existing backoff mechanisms force WTRUs that have received a NACK on theAICH to wait for some time before attempting to access the RACH again,starting the procedure from the beginning. The backoff mechanism reducesthe probability of having several WTRUs trying to access the channel atthe same time when the channel becomes free again.

When a Node B responds to a WTRU with a NACK because the resourceindexed by the implicit allocation is busy, it is likely that otherresources are free. The probability of this happening is even higher forlonger lookup tables. To avoid unnecessary delays, MAC-level RACHprocedures may allow multiple trials at requesting resources before thebackoff mechanism is triggered.

FIG. 4 is a flow chart showing a RACH method 400. At step 401, a firstpreamble phase is transmitted by a WTRU. At step 402, the Node Breceives the signal. If the Node B detects the preamble signaturesequence, at step 404, the Node B may transmit an ACK if the resourcerequested by the WTRU is available. If the Node B does not receive thesignal, it is in discontinuous transmit mode (DTX), and the Node B doesnot transmit an ACK or a NACK. If the Node B detects the preamble, butcannot allocate a resource, at step 406, the Node B transmits a NACK. Atstep 408 the WTRU determines if the maximum number of attempts after thefirst NACK has been reached. If the maximum is reached, at step 410, theWTRU institutes a back off routine. If the maximum is not reached, atstep 412 and index is updated and, at step 414, the WTRU retriesaccessing the RACH with a different preamble in a subsequent accessslot. The transmission power can be raised or kept the same. At step416, the Node B again attempts to detect the preamble. If detected, andthe resource is available, at step 418, an ACK is transmitted to theWTRU. If no resource is available, the Node B transmits and NACK and thechecking for maximum number of transmissions repeats at step 406. If theNode B does not detect the preamble, it is in DTX mode, and does notsend an ACK or a NACK at step 420 a backoff mechanism may be triggeredby the WTRU. The maximum number of attempts following a NACK can beconfigured by the network or predefined.

The resources associated with the E-DCH transmission phase may beexplicitly allocated. The transmission of an allocation message containsa subset of the E-DCH configuration, while the remaining configurationmay be signaled on the broadcast channel or preconfigured. Theallocation message is important and should be transmitted over the radiolink with protection. This may require acknowledgment from the WTRU.

The allocation message may be transmitted via an enhanced forwardacquisition channel (E-FACH), using high speed downlink shared channel(HS-DSCH) mechanisms. The WTRU identity may be related to the preamblesignature sequence or E-PRACH that was used, with a specified timingrelative to the access slot. For example, a set of temporary radionetwork temporary identifiers (t-RNTI) may correspond to each E-PRACHand may be broadcast to all WTRUs in a cell. Alternatively, a specificrule for implicit assignment of the t-RNTI could be defined.

The network may use a streamlined E-RACH message transmission phaseafter the RACH preamble phase. Rather than providing the full set ofE-DCH functionalities, only a subset of these functionalities are used.The reduced set of functionalities can be signaled and configuredthrough system information broadcasts.

All remaining parameters may be signaled through the system informationblock (SIB). This may include, for example, the UL scrambling code,enhanced dedicated physical downlink channel (E-DPDCH) configurationinformation, dedicated physical control channel (DPCCH) configurationinformation, radio bearer information for the logical channels mapped tothe E-RACH, and the like.

The E-RACH can be configured to operate in IDLE mode and to send an RRCCONNECTION REQUEST, or to operate in CELL_FACH state after a cellreselection, in order to send a CELL UPDATE message.

The WTRU may “append” scheduling information to the preamble. This canbe a reduced version of scheduling information (SI) and may provide anindication as to the buffer status and the available power headroom. Toreduce the number of bits required to signal this information, the WTRUmay use a coarse estimate of both of the parameters and encode theparameters in [X] bits, where X is an integer value.

A mapping can be constructed between the SI and the preamble signaturesequence. The choice of a signature sequence by the WTRU may be directedby the calculated SI. By way of example, if a 2 bit SI is used, 16signature sequences (sig_seq_(—)0 to sig_seq_(—)15) can be divided into4 groups (sig_group0 to sig_group3) each with 4 unique signaturesequences. The SI may be used to select one of the signature groups, andthe WTRU may randomly choose one of the sequences within that group.Upon decoding the signature sequence, the Node B may cross-reference thesequence number to determine the signature group, and as a result, thetransmitted SI. The Node B may send an acquisition indication. Theidentity of the WTRU may be determined when the Node B decodes the RACHmessage.

If the size of the SI exceeds 16, the number of preamble signatures canbe increased from 16 to 2̂k (where k>4). Rather than repeating thesequence 256 times in every preamble, the WTRU may repeat the newsequence (256/(2̂(k−4)) times.

FIG. 5 shows an alternative embodiment of the SI position 500. The SI504 can be appended at the end of each preamble 506. The preambleincludes 256 copies of a 16-bit signature sequence 502. The Node B maysearch for the preamble 506. When the preamble 506 is detected, the NodeB may detect the SI 504 at the end of the preamble 506 and send anacquisition indication. The identity of the WTRU may also be appended asa trailer.

After the WTRU receives an acquisition indication, it can send anotherpreamble at the same transmission power. The SI information can beappended to this preamble using coding of the signature sequence orappended to a trailer.

Alternatively, a second signature can be used in the repeat preamble,with a mapping rule between the first and second signature sequences.The mapping rule can be used by the Node B to determine the transmittedSI. As a benefit, the time offset between the two preambles can be hardcoded or configured through system information broadcasts and used bythe Node B to perform coarse uplink synchronization.

Grant information may be conveyed to the WTRU using the AICH or similarchannel. The RAN may take advantage of the acquisition indication thatis sent after the preamble acquisition to indicate to the WTRU themaximum transmission rate. FIG. 6 shows an AICH structure 600 inaccordance with one embodiment. The AICH 600 includes, per 20 ms TTI,access slot AS_0 (602) through AS_14 (604). Each AS_i 606, where i is aninteger between 0 and 14, includes, using SF256 channel coding, 40real-value signals 608. The last 1024 chips 610 of AS_i 606 include 8real-value grants, g_0 (612) through g_7 (614). Alternatively, the last1024 chips 610 may include control information.

A predefined sequence of symbols, e.g., a signature sequence, can bedefined for each of the control information levels. The mapping betweensymbol sequence and control information index may be known at the radioaccess network (RAN) and the WTRU. This mapping can be broadcast by theRAN, configured through higher layer signaling, or preconfigured.

Alternatively, the last 1024 chips of the AICH slot can be interpretedas a new bit field (e.g., 4 bits) which contains the index of the grantinformation, where channel coding can be used to increase decodingreliability of the bit field.

Alternatively, the grant information can be sent via a new physicallayer signal.

Metrics or parameters may be used, individually or in any combination,as a grant for initial E-RACH message transmission. One such parameteris the maximum power ratio, which indicates the maximum power ratiobetween the E-DPDCH and E-DPCCH or the maximum power ratio between theE-DPDCH and the preamble power.

The maximum transmission power may be used. This may indicate themaximum total power that the WTRU can use for transmission of theE-DPDCH. The maximum total power can be determined as an absolute value(e.g., 20 dBm) or as a relative power with respect to the preamblepower.

The value of the grant may be mapped to an index, where the mapping isknown by the WTRU and UTRAN. The mapping can be broadcast over systeminformation or hard coded in WTRU devices.

While in the CELL_DCH state, the WTRU identity is implicit since theWTRU has a dedicated connection. In the other states, the uplink channelis shared and the Node B has no means to identify the WTRU before themessage part content is decoded. In the context of the E-RACH, the WTRUidentity can be used by the Node B for the downlink transmission ofcontrol and data messages, and for collision detection.

The WTRU identity may be associated to the E-PRACH channel that is used.As such, the identity for each E-PRACH can be signaled by the Node B onthe broadcast channel, as part of the allocation table. Linking theidentity to the E-PRACH can be particularly useful in idle mode, wherethe WTRU has no resource or identity that has been assigned from thenetwork.

Alternatively, the WTRU RNTI may not be directly linked to the E-PRACH.If the WTRU is already in the CELL_FACH state, it may retain its E-RNTI.This identity may be maintained for radio transmission on the E-RACH andassociated control channels. If the WTRU does not already have an RNTIassigned by the network, such as when the WTRU is in idle mode, the WTRUmay generate a random identity that is signaled to the network on thefirst radio access in the E-RACH message part. For example, the randomlygenerated identity could be included as part of a medium access control(MAC-e) protocol data unit (PDU). In case the identity is already in useby another WTRU, the Node B may force the termination of the E-RACHmessage part transmission.

Alternatively, if the WTRU does not already have a RNTI assigned by thenetwork, the WTRU could generate an identity based on its internationalmobile subscriber identity (IMSI) or another unique identifier.

Although the features and elements are described herein in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmware tangiblyembodied in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) module.

What is claimed is:
 1. A method of allocating resources to a wirelesstransmit receive unit (WTRU) in CELL_FACH state or IDLE mode, the methodperformed by the WTRU and comprising: transmitting a signature sequence;receiving an acknowledge signal in response to the signature sequence;receiving an allocation message, wherein the allocation messageindicates a first subset of a set of enhanced dedicated channel (E-DCH)resource allocation parameters; receiving, via a broadcast channel, asystem information block (SIB) indicating a second subset of the set ofE-DCH resource allocation parameters; and configuring the WTRU forenhanced uplink transmission using a combination of the first subset andthe second subset.
 2. The method of claim 1, wherein the acknowledgesignal is an acquisition indicator (AI) received on an acquisitionindicator channel (AICH).
 3. The method of claim 1, wherein the firstsubset of the set of E-DCH resource allocation parameters is based on anaccess class of the WTRU.
 4. The method of claim 1, wherein the secondsubset of the set of E-DCH resource allocation parameters includescommon E-DCH parameters.
 5. A wireless transmit receive unit (WTRU),comprising: a transmitter configured to transmit a signature sequence; areceiver configured to receive an acknowledge signal in response to thesignature sequence; receive an allocation message, wherein theallocation message indicates a first subset of a set of enhanceddedicated channel (E-DCH) resource allocation parameters; and receive,via a broadcast channel, a system information block (SIB) indicating asecond subset of the set of E-DCH resource allocation parameters; and aprocessor configured to configure the WTRU for enhanced uplinktransmission using a combination of the first subset and the secondsubset.
 6. The WTRU of claim 5, wherein the acknowledge signal is anacquisition indicator (AI) received on an acquisition indicator channel(AICH).
 7. The WTRU of claim 5, wherein the first subset of the set ofE-DCH resource allocation parameters is based on an access class of theWTRU.
 8. The WTRU of claim 5, wherein the second subset of the set ofE-DCH resource allocation parameters includes common E-DCH parameters.9. A method performed by a base station, comprising: receiving asignature sequence from a wireless transmit receive unit (WTRU);transmitting an acknowledge signal to the WTRU in response to thesignature sequence; transmitting an allocation message to the WTRU,wherein the allocation message indicates a first subset of enhanceddedicated channel (E-DCH) parameters; and transmitting, via a broadcastchannel, a second subset of E-DCH parameters to the WTRU.
 10. The methodof claim 9, wherein the acknowledge signal is an acquisition indicator(AI) received on an acquisition indicator channel (AICH).
 11. The methodof claim 9, wherein the first subset of E-DCH parameters is based on anaccess class of the WTRU.
 12. The method of claim 9, wherein the secondsubset of E-DCH parameters includes common E-DCH parameters.
 13. A basestation, comprising: a receiver configured to receive a signaturesequence from a wireless transmit receive unit (WTRU); and a transmitterconfigured to: transmit an acknowledge signal to the WTRU in response tothe signature sequence; transmit an allocation message to the WTRU,wherein the allocation message indicates a first subset of enhanceddedicated channel (E-DCH) parameters; and transmit, via a broadcastchannel, a second subset of E-DCH parameters to the WTRU.
 14. The basestation of claim 13, wherein the acknowledge signal is an acquisitionindicator (AI) received on an acquisition indicator channel (AICH). 15.The base station of claim 13, wherein the first subset of E-DCHparameters is based on an access class of the WTRU.
 16. The base stationof claim 13, wherein the second subset of E-DCH parameters includescommon E-DCH parameters.